A liquid crystal display device is widely utilized for a display of a personal computer, a television and so forth. The device utilizes optical anisotropy and dielectric anisotropy of a liquid crystal compound. As an operating mode of the liquid crystal display device, various modes are known, such as a phase change (PC) mode, a twisted nematic (TN) mode, a super twisted nematic (STN) mode, a bistable twisted nematic (BTN) mode, an electrically controlled birefringence (ECB) mode, an optically compensated bend (OCB) mode, an in-plane switching (IPS) mode, a vertical alignment (VA) mode and a polymer sustained alignment (PSA) mode.
Among the modes, the ECB mode, the IPS mode, the VA mode and so forth are based on the operating mode utilizing vertical alignment of liquid crystal molecules. In particular, the IPS mode and the VA mode are known to have capability of improving narrowness of viewing angle being a disadvantage of the operating mode such as the TN mode and the STN mode.
In a liquid crystal display device to be operated according to the IPS mode and the VA mode, a liquid crystal composition having a negative dielectric anisotropy is mainly used. In order to further improve characteristics of the device, the liquid crystal compound contained in the liquid crystal composition preferably has physical properties as shown in (1) to (8):                (1) high stability to heat, light and so forth;        (2) high clearing point;        (3) low minimum temperature of a liquid crystal phase;        (4) small viscosity (η);        (5) suitable value of optical anisotropy (Δn);        (6) large negative value of dielectric anisotropy (Δ∈);        (7) suitable elastic constant (K33: bend elastic constant); and        (8) excellent solubility in other liquid crystal compounds.        
An effect of the physical properties of the liquid crystal compound on the characteristics of the device is as described below.
A compound having a high stability to heat, light and so forth as described in (1) increases a voltage holding ratio of the device. Thus, a service life of the device becomes long. A compound having a high clearing point as described in (2) extends a temperature range in which the device can be used. A compound having a low minimum temperature of the liquid crystal phase such as a nematic phase or a smectic phase as described in (3), particularly, a compound having a low minimum temperature of the nematic phase, also extends the temperature range in which the device can be used. A compound having a small viscosity as described in (4) shortens a response time of the device.
A compound having a suitable optical anisotropy as described in (5) improves a contrast of the device. According to a design of the device, a compound having a large optical anisotropy or small optical anisotropy, more specifically, a compound having a suitable optical anisotropy is required. When a response time is shortened by decreasing a cell gap of the device, a compound having a large optical anisotropy is suitable. A compound having a large dielectric anisotropy as described in (6) decreases a threshold voltage of the device. Thus, an electric power consumption of the device becomes small.
With regard to (7), a compound having a large elastic constant shortens a response time of the device; and a compound having a small elastic constant decreases a threshold voltage of the device. Accordingly, a suitable elastic constant is required according to characteristics to be desirably improved.
A compound having an excellent solubility in other liquid crystal compounds as described in (8) is preferred. The reason is that physical properties of the liquid crystal composition are adjusted by mixing liquid crystal compounds having different physical properties.
Various kinds of liquid crystal compounds having a large dielectric anisotropy have been synthesized so far. The reason is that (i) excellent physical properties that are not developed by a conventional compound are expected for a new compound, and that (ii) a suitable balance between two of arbitrary physical properties of the physical properties required upon preparing the liquid crystal composition is expected for a new compound.
For example, as disclosed in Patent literature No. 1, examples of reports have been found so far for a phenolic compound having a phenolic moiety, and a carbonyl group bonded with a carbon atom in a benzene ring of the phenolic moiety. However, the examples are limited to a compound having a relatively small negative value of dielectric anisotropy.